05-Wcdma Rf Optimization

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WCDMA RF Optimization

ISSUE 1.0

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This lecture introduces the various stages involved in optimizing a 3G radio network and focuses mainly on the RF Optimization phase.

Step-by-step approach for the analysis of drive survey data collected by Agilent Scanner and test UE is presented. The analysis is carried out using the post processing tool “Actix Analyzer”.

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RF optimization will be an ongoing activity and will need to be revisited as traffic increases in the network and as new sites are deployed.

In addition, as the network matures, the optimization process should be enhanced to take into account statistical data and key performance indicators collected throughout the network.

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Chapter 1 Chapter 1 Optimization PhasesOptimization Phases

Chapter 2 RF Optimization

Chapter 3 RF Analysis Approaches

Chapter 4 Antenna Adjustment Example

Chapter 5 Drop Call Analysis Example

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Network Optimization Phases – Flow ChartNetwork Optimization Phases – Flow Chart

New Site Integrated

Single Site Verification

RF Optimization

Cluster of Sites Ready?

Service Test and Parameter Optimization

Regular Reference Route Testing and Stats Analysis

Re-optimization Needed?

Y

N

N

Y

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Network Optimization Phases – Step 1Network Optimization Phases – Step 1

Single Site Verification To verify the functionality of every new site.

Objectives To ensure there are no faults related to site installation or

parameter settings.

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RF Optimization Once all the sites in a given area are integrated and

verified, RF (or Cluster) optimization could begin. Objectives

To optimize coverage while in the same time keeping interference and pilot pollution under control over the target area. This phase also includes the verification and optimization of the 3G neighbor lists.

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Services Testing & Parameter Optimization To be conducted in areas of good RF conditions in order

to exclude any coverage issues. Such testing does not need to be performed for each cell but the drive route must include different clutter types and environments.

Objectives To assess the performance and identify any need for

specific parameter optimization.

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Regular Reference Route Testing & Stats Analysis Constant monitoring and evaluation of the network

performance can be based on field testing as well as network stats analysis.

Results of the regular analysis may necessitate re-visits to the RF optimization and/or parameters’ tuning.

Objectives To identify any new issues that could arise, for example,

as a result of increase in traffic or changes in the environment.

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Chapter 1 Optimization Phases

Chapter 2Chapter 2 RF OptimizationRF Optimization




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RF Optimization - PreparationRF Optimization - Preparation

Clutters RF optimization should be carried out for groups or

clusters of sites rather than on single site basis. Drive Routes

Cluster drive surveys should include the coverage areas of each cell and all the major roads and streets as well as any other important locations.

Tools Agilent scanner Qualcomm UE in continuous AMR call Actix Analyzer

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RF Optimization - RF Optimization - TargetsTargets

Item Requirements Comments

CPICH RSCPTarget ≥ - 85 dBm Corresponds to outdoor

measurements.Minimum -95 dBm

CPICH Ec/IoTarget ≥ -8 dB

Applicable for unloaded network.Minimum - 14 dB

Active Set size (estimated)

Target ≤ 3 Based on scanner data.

Pilot pollution

Max % < 10 %% of time a cell is seen as a pilot polluter.

Threshold 8 dBRelative to best server when cell is not in Active Set.

UE Tx power Max <15 dBm Assuming 21 dBm max.

SHO Success rate Target >95 % For e1a, e1b & e1c

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RF Optimization – Flow ChartRF Optimization – Flow Chart

Drive TestDrive Test

Identify any RF IssuesIdentify any RF Issues

Identify candidate cells for changes

Identify candidate cells for changes

Identify nature of required changes

Identify nature of required changes

Determine amount of changes

Determine amount of changes

Implement changesImplement changes

Repeat Drive TestRepeat Drive Test

FinishFinish

N

Problem Resolved?Problem Resolved?

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RF Optimization - SolutionsRF Optimization - Solutions

Antenna tilt

Antenna azimuth

Antenna location

Antenna height

Antenna type

Site location

New site

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Chapter 3Chapter 3 RF Analysis ApproachesRF Analysis Approaches



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RF Analysis Approaches – Cell DominanceRF Analysis Approaches – Cell Dominance

Cells with no dominance at all A site was not radiating during the drive survey Very poor dominance can also be caused by blocking of

the antenna. So a site visit must be made to verify the antenna clearance.

Cells with either excessive or poor dominance This could be due to a high site or non-optimum antenna

tilts. Cells with too large dominance will be causing

interference to adjacent cells resulting in poor capacity.

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Areas of non-dominance: Areas where there is not a single clear dominant cell and

where the best server changes too frequently. Result: Excessive soft handover events reduce the

system efficiency and increas the probability of call drops.

UE vs. Scanner Best Serving Cells: Comparison between the UE and scanner SC plots.

Significant differences between the plots may indicate a missing neighbor or failed soft handoff problem.

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RF Analysis Approaches – RF Analysis Approaches – CPICH Coverage CPICH Coverage

Check areas of poor coverage, suggestion value as below: Good: RSCP ≥ -85 dBm Fair: -95 dBm ≤ RSCP < -85 dBm Poor: RSCP < - 95 dBm

Examine the RSCP coverage on per cell bases in order to highlight any cells that have too large a footprint.

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RF Analysis Approaches – RF Analysis Approaches – CPICH CoverageCPICH Coverage

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RF Analysis Approaches – RF Analysis Approaches – InterferenceInterference

CPICH Ec/Io Plot Good: Ec/Io ≥ -8 dB Fair: -14 dB ≤ Ec/Io < -8 dB Poor: Ec/Io < - 14 dB

The -8 dB threshold takes into account the expected future interference increase as a result of increased traffic.

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Because the RSCP Level is poor, and the fundamental cause of low Ec/Io is poor coverage

Because the RSCP Level is poor, and the fundamental cause of low Ec/Io is poor coverage

-15.5

-104

-20

-19

-18

-17

-16

-15

-14

Ec/Io RSCP-120

-115

-110

-105

-100

-95

-90

What’s the problem?

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RSCP level is good, and this will imply strong system interference

RSCP level is good, and this will imply strong system interference

-15.5

-63

-20

-19

-18

-17

-16

-15

-14

Ec/Io RSCP-90

-85

-80

-75

-70

-65

-60 What’s the problem?

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RF Analysis Approaches – UL CoverageRF Analysis Approaches – UL Coverage

Uplink Coverage (UE Tx Power) High UE Tx power means possible poor uplink coverage. Areas of high Tx power should be compared to the CPICH pilots

to verify if the problem only exists on the uplink.

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RF Analysis Approaches – UL CoverageRF Analysis Approaches – UL Coverage

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RF Analysis Approaches – Pilot PollutionRF Analysis Approaches – Pilot Pollution

Pilot Pollution Point Define: Not all points in the active set Within a certain margin of the best server( the margin is

set to 8dB)Cells which are frequently seen as polluters (e.g. >8% time)

should be marked and investigated. Pilot Pollution results should be used in conjunction with the

Estimated Active Set Size

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-62 -64 -66 -68 -69

-81

-90

-85

-80

-75

-70

-65

-60

SC1 SC2 SC3 SC4 SC5 SC6

RSC

P (d

Bm)

Active Set Pilot Pollution

Margin

NotPilot Pollution

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SC Count % in Pollution Set8 206 12.9%9 165 10.3%

10 157 9.8%11 156 9.7%12 148 9.2%13 135 8.4%16 95 5.9%17 94 5.9%18 76 4.7%19 74 4.6%20 73 4.6%21 56 3.5%32 54 3.4%35 39 2.4%37 33 2.1%43 19 1.2%48 8 0.5%53 7 0.4%67 3 0.2%80 2 0.1%

130 2 0.1%

Should be investigated

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Estimated Active Set Size Another useful measure of pilot pollution is by looking at

the estimated active set based on the scanner data. This plot is obtained by modeling the network soft handoff parameters within Actix.

In order to see areas of excessive SHO candidates, the estimated active set size is allowed to exceed maximum of 3.

This can be done in conjunction with the Pilot pollution analysis.

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Estimated Active Set Size Example

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RF Analysis Approaches – Neighbor ListRF Analysis Approaches – Neighbor List

Neighbor List Verification The neighbor list could be verified and optimized using

the Neighbor List Verification tool within Actix. Recommendations for Each Cell:

Retain: This indicates that those neighbors have been confirmed from the drive survey data.

Add: Missing neighbors Remove: These neighbors that were not measured but

are in the neighbor list.

Careful consideration is needed prior to removing neighbours since the Actix results are drive route dependent.

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RF Analysis Approaches – Neighbor ListRF Analysis Approaches – Neighbor List

Neighbor List Verification Example

009 576 Retain 018 82 14.2%Retain 010 46 8.0%Retain 016 31 5.4%Retain 032 20 3.5%Retain 011 18 3.1%

Add 130 17 3.0%Retain 021 17 3.0%Retain 008 12 2.1%Retain 020 6 1.0%Retain 012 5 0.9%Retain 017 2 0.3%

Remove 053 0 0.0%Remove 019 0 0.0%Remove 034 0 0.0%Remove 037 0 0.0%Remove 013 0 0.0%Remove 051 0 0.0%

70548 Ajman Central 25.41204 55.447

Nbr SCSample Count

%Latitude LongitudeSample Count

ActionSC Cell Site

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RF Analysis Approaches – SHORF Analysis Approaches – SHO

UE SHO Performance The success rates for event 1a, 1b & 1c and can be

obtained from Actix Number of Active Set Updates

Event CountEvent 1a - Cell Addition328Event 1b - Cell Removal306Event 1c - Cell Replacement64

Number of Active Set Update Completes

Event CountEvent 1a - Cell Addition326Event 1b - Cell Removal305Event 1c - Cell Replacement62

Soft-Handover Success Rate

Event RateEvent 1a - Cell Addition99.4Event 1b - Cell Removal99.7Event 1c - Cell Replacement96.9

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RF Analysis Approaches – Call DropRF Analysis Approaches – Call Drop

Drop Call Analysis - RF related issues : Poor coverage (RSCP & Ec/Io) High interference and hence poor Ec/Io Poor uplink coverage (insufficient UE Tx power) Poor dominance (best cell changes too frequently

resulting in too many SHO events) Pilot pollution (too many cells present) Missing neighbors Fast change of RF conditions (e.g. turning a corner)

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Drop Call Analysis Example 1

Call Drop

RSCP & Ec/Io degrades BOTH for scanner and UE

Check for Coverage problems

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Call Drop

Ec/Io (and RSCP) degrades for UE ONLY while scanner shows no degradation

Ec/Io (and RSCP) degrades for UE ONLY while scanner shows no degradation

UE camp on new cell immediately after drop, and UE did not

measure this cell before Drop

UE camp on new cell immediately after drop, and UE did not

measure this cell before Drop

Check the NeighborCheck the Neighbor

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Call Drop

Too many and too quick changes of best server

Too many and too quick changes of best server

UE to perform measurements and SHO in time difficultly

UE to perform measurements and SHO in time difficultly

Ping-Pong Handover, need to improve cell dominance

Ping-Pong Handover, need to improve cell dominance

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Chapter 4Chapter 4 Antenna Adjustment ExampleAntenna Adjustment Example


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Antenna Adjustment ExampleAntenna Adjustment Example

RSCP Coverage before Adjustment

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RSCP Coverage after Adjustment

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RSCP Distribution

CPICH RSCP Distribution

1.44

%

20.3

1% 29.3

3%

30.2

7%

18.6

5%

0.02

%

5.47

%

25.9

8%

31.0

4% 37.4

8%

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

30.00%

35.00%

40.00%

Before Adjustment After Adjustment

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Down Tilt from 4 to 6 Result

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Down Tilt from 4 to 8 Result

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Chapter 5Chapter 5 Drop Call Analysis ExampleDrop Call Analysis Example

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Call Drop Analysis ExampleCall Drop Analysis Example

Call Drop Distribution

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There are total 5 drop calls in the plot.

The example of drop call 1 is analyzed to show the process of analysis in the following.

Call drop 1 occurred at an area of frequent change of best server as shown by the scanner scrambling code plot

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CPICH RSCP and Ec/Io before the Call Drop

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Compare Ec/Io from both scanner and UE at the time of the drop as shown in Figure. This clearly shows the UE Ec/Io to drop to < -21 dB while the scanner remained above -11 dB.

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Best server before and after the Call Drop

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Comparing the best servers from the UE and the scanner at the time of drop:

Call Drop 1 (UE vs. scanner best server) shows that SC008 is the best server before call drop in both UE and scanner. However, about 30 seconds before the drop, the scanner selected SC018 as the best server while the UE continued to have only SC009 in its active set resulting in the drop call. Immediately after the drop, the UE camps on SC018.

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UE Active Set and Monitor Set Before and After the Call Drop

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Conclusion Examining the UE Active and Monitored set, Figure does not

show SC018 to be measured by the UE prior to the drop. This scenario resembles a missing neighbor problem

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Coverage of Call Drop Point

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Solution: Looking at call drop Figure clearly shows that at the

location of the drop, SC018 should not be the best server.

Cell SC018 clearly requires some down tilting to control its interference into the area of Drop 1. To illustrate this, RSCP coverage of SC018 shows clearly that the cell’s is extending into a large area. E.g. around the location of drop call, SC018 RSCP is > -75dBm.

Add the Missing Neighbors

05-Wcdma Rf Optimization

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